1. Field of the Invention
The present invention relates to a method of blanking elements of a belt for use in a continuously variable transmission.
2. Description of the Prior Art
As shown in FIGS. 1(a) and 1(b) of the accompanying drawings, an element 1 of a belt for use in a continuously variable transmission comprises a body 2 which, when a plurality of elements 1 are stacked and bundled into an annular form, will be positioned radially inside of the annular form, i.e., on a lower side in FIGS. 1(a) and 1(b), and a head 4 joined to the body 2 by a neck 3, to be positioned radially outside of the annular form. Between the head 4 and the body 2 that are positioned on the opposite sides of the neck 3, there are defined two recesses 5 in which endless rings, not shown, will be mounted to bundle the elements 1 into the annular form. The body 2 has on its lower reverse side a slanted surface 6 that is progressively tapered downwardly away from the head 4 and a thin portion 7 extending from the slanted surface 6 toward the lower end of the body 2.
The element 1 is usually formed by blanking, with a blanking punch, an elongate metal sheet placed on a die of an element manufacturing apparatus and having a thin portion joined to the rest of the metal sheet via a corner. The corner of the metal sheet is machined into the slanted portion 6 on the reverse side of the element 1 by a counter punch that is held against the reverse side of the element 1. A plurality of blanked elements, e.g., several hundred elements, are stacked and bundled into an annular form by endless rings mounted in the recesses in the elements, producing a belt assembly for use in a continuously variable transmission. Since the belt assembly is constructed of a number of stacked elements, it is important to manage the thicknesses of the elements. If the thicknesses of the body 2 and the head 4 are widely different from each other, for example, then the belt assembly is vertically distorted when the elements are stacked together. If the elements suffer large thickness variations in their transverse direction, then the belt assembly is laterally distorted when the elements are stacked together. The elements should be manufactured with increased productivity because a number of elements are needed to produce an element assembly.
When an element is blanked out of the metal sheet, the corner of the metal sheet is machined into the slanted surface. In order to keep the thickness of the element in an allowable range, it is necessary to position the metal sheet with increased accuracy at the time of blanking the element out of the metal sheet. However, productivity tends to be lowered if the metal sheet is positioned with increased accuracy.
Consequently, there has been a demand in the art for a process of blanking elements with increased productivity and a good yield.
It is therefore an object of the present invention to provide an improved method of blanking elements of a belt for use in a continuously variable transmission.
Another object of the present invention is to provide a method of blanking elements of a belt for use in a continuously variable transmission with increased productivity and a good yield.
When elements are blanked out of two opposite sides of an elongate metal sheet, the metal sheet may possibly be displaced transversely, and thickness variations of individual elements may possibly fall out of an allowable range. The inventor of the present invention has found that even if the metal sheet is displaced transversely and thickness variations of individual elements fall out of an allowable range, when the elements blanked from the opposite sides of the metal sheet are mixed at a ratio of about 1 to 1 into a belt assembly, the belt assembly thus constructed poses no problems for use in a continuously variable transmission.
According to the present invention, a method is provided for blanking elements of a belt for use in a continuously variable transmission, each having a body and a head joined to the body by a neck, the body having a slanted surface tapered away from the head and a thin portion extending from the slanted surface toward an end of the body remote from the head. In this method, an elongated metal sheet is prepared having a flat central portion extending longitudinally and a pair of thin portions disposed on a reverse side thereof and extending from respective corners at edges of the flat central portion toward opposite edges of the elongated metal sheet. Element blanking punches are applied to a face side of the elongated metal sheet, which is placed on a die to blank elements having heads confronting each other across the elongated metal sheet out of two opposite sides thereof, and counter punches are applied to the corners on the reverse side of the elongated metal sheet and movable with the element blanking punches to deform the corners of the elongated metal sheet under a counter load into slanted surfaces of the elements. Averages of the differences between thicknesses of blanked elements are determined at a measurement point positioned at or near the neck above the slanted surface and below the head and a measurement point positioned at the head. The distance between the corners of the elongated metal sheet and the counter load are established in order to keep the averages in a predetermined allowable range. Elements are then blanked out of the opposite sides of the elongated metal sheet with the established distance between the corners thereof, with the element blanking punches and the counter punches under the established counter load.
In the above method, the differences between thicknesses at certain points on individual elements are not managed, but the averages of the differences between thicknesses at certain points on elements blanked out of the opposite sides of the metal sheet are managed and brought into a given allowable range. Variations of the averages of the differences between thicknesses at certain points on elements blanked out of the opposite sides of the metal sheet with their heads confronting each other cancel each other. Therefore, even if the differences between thicknesses of individual elements do not fall out of an allowable range, a belt assembly constructed of these elements poses no problems for use in a continuously variable transmission. Thus, elements can be manufactured with a good yield. Since the metal sheet can be positioned with less accuracy when the elements are blanked out of the metal sheet than if the thicknesses of individual elements are managed, the elements can be manufactured with increased productivity.
The averages of the differences between thicknesses are adjusted based on the distance between the corners and the counter load. By averaging the differences between thicknesses at a measurement point positioned at the neck or nearly at the neck above the slanted surface and below the head and a measurement point positioned at the head, a belt assembly constructed of stacked elements is prevented from being distorted vertically.
In the method according to the present invention, each of the elements preferably has a pair of ears extending laterally from a center of the head, and the measurement point positioned at the head preferably comprises measurement points positioned respectively on the ears. Because the ears are positioned laterally of the head, when the average of the differences between thicknesses of the ears is brought into a given allowable range, a belt assembly constructed of stacked elements is prevented from being distorted horizontally.
In the method according to the present invention, the step of determining averages of the differences between thicknesses of blanked elements preferably comprises the step of determining the averages when the elements blanked from the two opposite sides of the elongated metal sheet are mixed at a ratio of about 1 to 1. Inasmuch as the elements are blanked from the two opposite sides of the elongated metal sheet, if the average of the differences between thicknesses of the elements blanked from one of the two opposite sides of the elongated metal sheet becomes larger, then the average of the differences between thicknesses of the elements blanked from the other of the two opposite sides of the elongated metal sheet becomes smaller. Therefore, if the elements blanked from the two opposite sides of the elongated metal sheet are mixed at a ratio of about 1 to 1, then variations of the averages of the differences between thicknesses of those elements cancel each other. With the heads thus constructed, therefore, thicknesses of the ears at certain locations thereof are measured.
In the method according to the present invention, the step of determining averages of the differences between thicknesses of blanked elements preferably comprises the step of determining the averages when the elements blanked from the two opposite sides of the elongate metal sheet are mixed at a ratio of about 1 to 1. Inasmuch as the elements are blanked from the two opposite sides of the elongate metal sheet, if the average of the differences between thicknesses of the elements blanked from one of the two opposite sides of the elongate metal sheet becomes larger, than the average of the differences between thicknesses of the elements blanked from the other of the two opposite sides of the elongate metal sheet becomes smaller. Therefore, if the elements blanked from the two opposite sides of the elongate metal sheet are mixed at a ratio of about 1 to 1, then variations of the averages of the differences between thicknesses of those elements cancel each other.
In the method according to the present invention, the step of establishing a distance between the corners and the counter load preferably comprises the steps of setting the distance between the corners to a value in order to keep the averages of the differences between thicknesses in an allowable range within an adjustable range of the counter load, and adjusting the counter load in order to reduce the averages of the differences between thicknesses when the elements are blanked.
To change the distance between the corners of the metal sheet, it is necessary to change the shape of the metal sheet. Therefore, if the metal sheet is produced by dies, then the dies need to be changed in shape. The counter load may be changed by changing forces with which the counter punches are biased. Therefore, the distance between the corners is established within the adjustable range of the counter load. Thereafter, elements are actually blanked out of the metal sheet, and the counter load is then adjusted in order to reduce the averages of the differences between thicknesses. In this manner, the averages of the differences between thicknesses can easily be reduced.
The thin portions of the elongated metal sheet may be slanted from the corners toward opposite edges of the elongated metal sheet, or may extend flatwise from the corners toward opposite edges of the elongated metal sheet.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.